The present invention pertains generally to selectable impedance circuits for effectuating control functions and specifically to a digital technique employable therewith.
Whenever equipment is to be controlled from a remote location to effectuate some mechanical control movement, it is common practice to employ an electrical feedback loop such as in a servo system whereby an electrical sensing signal at the controlled location changes in accordance with the desired mechanical motion thereat until brought into correspondence with an electrical control signal generated at the controlling location indicative of the mechanical change desired by the operator. One typical arrangement utilizes a bridge circuit comprising a pair of selectable impedance circuits consisting of a plurality of serially connected impedances and a selector which is connectable to any common junction of the impedances. With the end terminals of the circuits connected together to an electric signal source, one circuit is located at the controlling location while the other circuit is located at the controlled location to afford the desired remote control. By mechanically linking the controlled circuit selector to the mechanically controlled device and providing a position sensing signal thereat, the desired mechanical movement can be achieved by permitting the adjustment of the aforesaid selector until a null point which no longer effectuates the mechanical movement is attained upon comparison of the sensing signal with the electric control signal resulting from the setting of the controlling circuit selector. The foregoing arrangement is often found in avionics equipment wherein control knobs in the cockpit of the plane are adjusted to tune radios to desired frequencies either for voice communication or navigation purposes.
With the proliferation of digital electronics, particularly in radio communications, the economics of modernizing equipment often dictate partial conversion without revamping the entire system. For example, in the remote control scheme alluded to in the preceding paragraph, it is not uncommon to justify conversion to avionics digital radio equipment only when the retrofit of the controlling equipment in the cockpit of the plane can be avoided. Consequently, a primary object of the present invention is to provide a digital indication for use with a selectable impedance control type circuit to afford digital rather than analog signals for effectuating control of digital type equipment.
It is a further object of the present invention to provide such a digital indication with a minimum of equipment so as to ameloriate the descriptive modification effects to existing equipment when retrofitting same.
The foregoing objects as well as others and the means by which they are achieved through the present invention may best be appreciated by referring to the Detailed Description of the Preferred Embodiment which follows hereinafter together with the single figure of the attached drawing which depicts the functional block elements of the invention.